Careful planning of the wireless cellular communication networks has been of high importance ever since the development of the early analog networks such as NMT and AMPS. A careful planning is equally important for today's cellular systems such as the WCDMA based UMTS and CDMA-2000, and will be as important in future systems.
As is well known, the often depicted hexagonal pattern of the base stations of a wireless network is a simplification. In reality, with for example a varying topography or a plurality of man-made obstacles such as tall houses, the demand for coverage almost everywhere, including indoors and underground etc, the planning of a network is far from trivial. In addition to the mentioned factors relating to the radio propagation properties a successful network planning must take into account the varying demands on capacity. In certain portions of the network, corresponding to densely populated areas, for example, the capacity must be higher than in more rural areas. This capacity need may shift during a day. During working hours the demand for capacity will typically be highest in for example office areas, while in the evenings and nights the demands will be very low.
The coverage area of a wireless network is defined as the area wherein the users have access to their subscribed services. It is vital both to the users and the operators of wireless network that the wireless system has adequate coverage.
In principle, improving coverage is simple, it is only a matter of deploying a sufficiently dense pattern of base stations. However, since the cost of a cellular system is to a very high degree proportional to the number of base stations, an operator tries to avoid over-dimensioning. The cost of a base station comes both from the equipment itself and its installation cost, but also to a high degree operation and maintenance costs and the cost for renting properties for the base stations. In addition environmental and esthetical issues have been raised concerning base station mast and antennas. Hence, operators strive to fulfill the coverage requirement using as few base stations as possible.
A vast number of methods and tools have been developed and deployed to estimate coverage. Three main approaches, which often are used in combination, in assessing the coverage of a network may be distinguished: propagation predictions; drive tests and traffic statistics.
Propagation predictions rely on very accurate map data, both with regards to the natural topography and to man made objects. This is an obvious starting point the planning a network, but can, although great improvements have been reported over the years, only give rough coverage predictions. This is particularly true for indoor environments.
Drive tests, which comprise of measuring the radio coverage in the field, typically by vehicle-based measuring units, give reliable data for the location of the measurement. However, to cover all parts of a network with a drive test is in practice impossible—the tests are typically confined to roads and the like. In addition, drive tests are time-consuming and expensive.
Traffic statistics are performed on a running network. Most commonly dropped calls are identified and related to a geographical area. However, the methods can not discern what caused the dropped call, and since there are many reasons for a dropped call apart from bad coverage, the dropped call statistics are a blunt instrument for cell planning purposes. In addition, a bad coverage does in certain network not necessarily, or immediately, lead to a dropped call, but degraded performance. Dropped call statistics does not account for these cases.
In practice the cell planning often involves all three approaches, the propagation predictions is performed as a first measure to plan the network; drive tests and traffic statistics are used in a later state to assess coverage of the existing network.
Cell planning has become even more complicated with the widespread use of CDMA-based access technology, such as WCDMA. CDMA systems will, due to interference-limited nature, exhibit dynamic cell coverage, i.e. the coverage of a cell will be dependent on the load in the cell. This behaviour, intrinsic to CDMA, is commonly referred to as cell breathing. Cell breathing can be accounted for in propagation predictions used for cell planning. EP 1,294,208 and U.S. Pat. No. 5,710,758 teach methods of improving commonly used simulation approaches in cell planning by incorporating the effects of cell breathing. The disclosed methods take cell breathing into account but have the drawback in common with the previously mentioned prediction methods that they for a real network, only give rough estimates of the real radio environment. Hence, methods and arrangement for improving the cell planning and/or uplink load control, based on traffic statistics and which handles the dynamic cell coverage is needed.
The technology disclosed herein provides methods and arrangement that facilitate an improved cell planning and/or improved uplink load control in cellular communication networks exhibiting dynamic cell coverage. In particular, the technology disclosed herein provides reliable traffic statistics in an up and running network.
The technology disclosed herein provides a method for estimating uplink coverage in a wireless communication system, which the exhibits load dependent cell coverage. The method gathers traffic statistics related to radio coverage in individual cells in a wireless communication system in operation, and comprises the steps of:                determining a received rate from at least one mobile terminal being in a communication session, by measuring the number of received transport blocks during a predetermined time interval; and        comparing the received rate with a predetermined expected rate, and if the received rate is below the expected rate, identifying poor coverage. Since the coverage is potentially load dependent an estimate of the uplink coverage has been obtained.        
Preferably, if the received rate is below the expected rate, an indication of insufficient coverage is stored for later analysis, either for cell planning purposes or radio resource management purposes such as uplink load control. Alternatively, or in combination with storing the indications of insufficient coverage, the received rate is stored. This part of the method according to an example embodiment is preferably performed in a radio network controller (RNC) node in the wireless communication system.
According to a first aspect of an example embodiment the method comprises a further step of performing a cell planning function using the stored indications on insufficient coverage and/or the stored received rates to identify areas with poor radio coverage. This is preferably performed in an O&M node which retrieves the gathered traffic statistics from the RNC.
According to a second aspect of an example embodiment the method comprises a further step of performing a load control function on the stored information to identify inadequate admission control thresholds by comparing the number of indications of insufficient coverage, or a ratio of transmissions giving rise to indications of insufficient coverage compared to the total number of transmissions, with a predetermined load value, said load control function performed per cell, and suggesting a lowering of the admission control threshold if the load control function has identified an inadequate admission control threshold for the cell. The load control function is preferably performed in the RNC.
According to a third aspect of an example embodiment the method of present invention the step of comparing comprises the substeps of:                comparing the received rate of a first TTI and the received rate of a second consecutive TTI with the expected rate;        determining if the received rate of the second TTI is zero, and storing an indication of insufficient coverage and/or the received rate only if the received rate of both the first and second TTI are below the expected rate and the rate of the second TTI is nonzero, whereby discerning between low received rate due an ending transmission and low received rate possibly due to poor coverage. In the case of low received rate due to an ending transmission the rate of first TTI may be below the expected rate, but the rate of consecutive second TTI will in that case be zero.        
Thanks to the technology disclosed herein it is possible to estimate the uplink coverage from traffic statistics in an up and running network in a way that does not require control signalling over the air interface.
One advantage afforded by the technology disclosed herein is that the method may be used for an improved cell planning as it gives an estimate of the load dependency of the cell coverage for the cells in the wireless system.
Yet another advantage afforded by the technology disclosed herein is the ability, according to one embodiment, to discern between low received rate due an ending transmission and low received rate possibly due to poor coverage.
A further advantage is that the technology disclosed herein can be utilized to improve the radio resource management procedure such as admission control.
Further advantages and features of example embodiments of the technology disclosed herein will become apparent when reading the following detailed description in conjunction with the drawings.